1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to an array substrate for In-Plane Switching (IPS) mode liquid crystal display device and fabricating method for the same in order to realize a minute pixel.
2. Discussion of the Related Art
A typical liquid crystal display (LCD) device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite orientation order in alignment resulting from their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by supplying an electric field to the liquid crystal molecules. In other words, as the alignment direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Because incident light is refracted to the orientation of the liquid crystal molecules due to the optical anisotropy of the aligned liquid crystal molecules, image data is displayed.
Currently, active matrix LCDs, in which the thin film transistors and the pixel electrodes are arranged in the form of a matrix, are widely used because of their high resolution and superiority in displaying moving images. An array substrate for the related art in-plane switching (IPS) mode liquid crystal display (LCD) device and the fabricating method for the same will be described hereinafter.
FIG. 1 is a plan view of a pixel of an array substrate for a related art in-plane switching (IPS) mode liquid crystal display (LCD) device. As shown in the figure, a plurality of gate lines 12 and common lines 16 are horizontally formed on an array substrate 10 and they are spaced apart from each other. A plurality of data lines 24 is vertically formed on the array substrate 10 and cross the gate lines 12 and the common lines 16. The data line 24 defines a pixel “P” by crossing the gate line 12. A thin film transistor “T” is formed in a cross point of the gate line 12 and the data line 24. The thin film transistor “T” includes a gate electrode 14, an active layer 20, a source electrode 26 and a drain electrode 28. The active layer 20, the source electrode 26 and the drain electrode 28 are formed over the gate electrode 14. The gate electrode 14 communicates with the gate line 12 and the source electrode 26 communicates with the data line 24. A pixel electrode 30 that communicates with the drain electrode 28 and a common electrode 17 that is parallel with the pixel electrode 30 are formed in the pixel region “P”. The common electrode 17 communicates with the common line 16. The pixel electrode 30 includes an extension portion 30a, a vertical portion 30b and a horizontal portion 30c. The extension portion 30a of the pixel electrode 30 is extended from the drain electrode 28 and the vertical portion 30b of the pixel electrode 30 is vertically extended from the extension portion 30a. The horizontal portion 30c of the pixel electrode 30 is formed over the common line 16 and connected to the vertical portion 30b. The common electrode 17 includes a horizontal portion 17a and a plurality of vertical portions 17b. The plurality of vertical portions 17b of the common electrode 17 is arranged in an alternating order with the vertical portion 30b of the pixel electrode 30. The horizontal portion 17a of the common electrode 17 connects the plurality of the vertical portion 17b into one portion. An auxiliary storage capacitor “C” is formed in the pixel region “P”. The auxiliary storage capacitor “C” uses a portion of the common line 16 as a first storage electrode and the horizontal portion of the pixel electrode 30c as a second storage electrode.
FIGS. 2A to 2C are cross-sectional views taken along II-II and III-III of FIG. 1 illustrating a fabrication process according to a fabrication sequence of the related art. In FIG. 2A, the gate line 12 of FIG. 1 including the gate electrode 14, the common line 16 and the common electrode 17 are formed on the substrate 10 by depositing and patterning conductive metal material such as aluminum (Al), aluminum neodymium (AlNd), chromium (Cr), molybdenum (Mo) or tungsten (W), for example. A gate insulating layer 18 is then formed on the substrate 10 by depositing inorganic insulating material such as silicon nitride (SiNx) or silicon oxide (SiO2), for example. The active layer 20 and an ohmic contact layer 22 are formed on the gate insulating layer 18 by depositing and patterning amorphous silicon (a-Si:H) and doped amorphous silicon (n+a-Si:H or p+a-Si:H).
In FIG. 2B, the data line 24, the source electrode 26, the drain electrode 28 and the pixel electrode 30 are formed on the substrate 10 by depositing and patterning conductive metal material such as aluminum (Al), aluminum neodymium (AlNd), chromium (Cr), molybdenum (Mo) or tungsten (W), for example. The data line 24 defines the pixel region “P” by crossing the gate line 12 and the common line 16. The source electrode 26 is formed by being extended from the data line 24 and partially overlapped with the active layer 20. The drain electrode 28 is spaced apart from the source electrode 26. The pixel electrode 30 comprises the extension portion 30a, the vertical portion 30b and the horizontal portion 30c. The horizontal portion 30b of the pixel electrode 30 is formed on the common line 16. The active layer 20 portion between the source electrode 26 and the drain electrode 28 is exposed by etching the ohmic contact layer 22 between the source electrode 26 and the drain electrode 28.
In FIG. 2C, a passivation layer 32 is formed on the substrate 10 by coating organic insulating material such as benzocyclobutene (BCB), for example, or by depositing inorganic insulating material such as silicon nitride (SiNx) or silicon oxide (SiO2), for example.
FIG. 3 is a circuit diagram of FIG. 1. A capacitor communicates with the thin film transistor “T” in series. The capacitor includes a liquid crystal capacitor (CLC) and a storage capacitor (CST), which is connected in parallel to the liquid crystal capacitor (CLC).
However, if the pixel structure stated above for the in-plane switching (IPS) mode liquid crystal display (LCD) device that drives a minute pixel, an area for the storage capacitor “C” is limited. Moreover, if the area for the storage capacitor “C” is designed to be larger in order to secure a capacitance of the storage capacitor “C”, an aperture ratio of the liquid crystal panel is decreased.